docs: def export_avg_losses_ebrisk(ekey, dstore):
      """
      :param ekey: export key, i.e. a pair (datastore key, fmt)
      :param dstore: datastore object
      """
      name = ekey[0]
      oq = dstore['oqparam']
      dt = oq.loss_dt()
      value = dstore[name].value  # shape (A, L)
      writer = writers.CsvWriter(fmt=writers.FIVEDIGITS)
      assets = get_assets(dstore)
      dest = dstore.build_fname(name, 'mean', 'csv')
      array = numpy.zeros(len(value), dt)
      for l, lt in enumerate(dt.names):
          array[lt] = value[:, l]
      writer.save(compose_arrays(assets, array), dest)
      return writer.getsaved()